Cell free DNA found in the blood and other bodily fluids can be used to detect and diagnose many genetic disorders. Numerous methods exist for non-invasive prenatal genetic diagnostics. Non-invasive prenatal genetic diagnoses can be performed on cell-free DNA, e.g., obtained from blood, from a patient. Cell-free DNA can also be used to detect or monitor the presence of tumor cells in patients. Such methods are complex to carry out and are subject to numerous errors resulting in imprecision and inaccuracy. It is important for commercial laboratories to demonstrate proficiency in testing in order to obtain regulatory approval for carrying out such tests. Accordingly, it is necessary for laboratories carrying out such procedures to engage in proficiency testing using standards for analysis. Such standard testing can be problematic given the relative scarcity of naturally occurring samples and the variability between such samples. Provided herein are methods and compositions for addressing this problem.